Hey James - I definitely will do the grill block (as well as other aero mod things) but not 'til I get a decent baseline of pre-aero mod FE. With the fuel fillup variability (as you mentioned and as I've discovered), it'll take a few tankfuls to get a baseline I can be confident with.
After I have a baseline, then I will do instrumentation to further refine my driving style, and after that I will start with the aero mods. I'm doing it this way intentionally because I know I'll be modifying my driving style regardless and didn't want to throw another variable into the overall FE progress. (I'd like to be able to highlight what changes have what FE impact.)
Of course resisting the urge to do simple aero mod stuff is going to be tough... So we'll see how well I can stick to my plan...
Switching to the Fed ECU is yet another variable, but I really do want that to be part of my baseline as well (i.e. pre-aero mods).
Though I don't have the shift light, I have been shifting as low as possible... most often under 2K rpm, and sometimes even under ~1300 rpm... very impressive how well the d15z1 engine can pull at those low rpms!